Zafirakis D', Kavadias K'A', Kaldellis J'K'

1
EWEC, 2008 European Wind Energy Conference
Brussels Expo, Belgium, 31 March - 3 April 2008
EVALUATION OF THE WIND-CAES ENERGY SOLUTION FOR
THE AEGEAN ISLANDS. THE CASE OF A PRIVATE WIND
PARK IN CRETE

• Zafirakis D., Kavadias K.A., Kaldellis J.K.
• Lab of Soft Energy Applications Environmental
  Protection, TEI of Piraeus
• e-mail sealab_at_gdias.teipir.gr URL
  http//www.sealab.gr
• Tel. [phone], FAX [phone]
• P.O. Box 41046, Athens 12201, Greece

2
INTRODUCTION
The Aegean Archipelago area is a remote area
comprising several scattered islands with an
excellent wind potential. The main problems of
the area concerning the exploitation of the local
wind potential are the significant electrical
grid constraints and the stochastic availability
of wind energy. As a result, only 10 of the
areas energy consumption is covered by the
operation of local wind parks.
3
CASE STUDY CRETE ISLAND(1/2)

• An interesting case study regards the island of
  Crete, the latter electrification system being
  based on the operation of
• 715 MW of thermal power plants
• 124.5 MW of wind parks (15 WP)
• 1.3 MW of hydropower and PV

Thermal Power Stations (2007)
4
CASE STUDY CRETE ISLAND(2/2)
Despite the excellent wind conditions, only 1/3
of onshore wind energy potential has been
exploited.
More specifically, the existing constraints of
the local network discourage new wind power
investments, while at the same time, financial
losses may be encountered for the already
operating wind parks.
5
FUTURE ENERGY PLANNING FOR CRETE
The introduction of natural gas in the local
energy balance provides a new opportunity for
increased wind energy exploitation. In this
context, a new installation of an LNG terminal in
Korakia is scheduled. Additionally, a production
licence has been approved for the installation of
a 250 MW combined cycle power unit in the area of
Korakia by 2012.
6
ALTERNATIVE ENERGY GENERATION PATTERNS REQUIRED
In an attempt to increase the participation of
wind energy in the local energy balance and
maximize the local wind potential exploitation,
we investigate a Wind-Compressed Air Energy
Storage (CAES) configuration. According to
several studies, wind energy storage suggests a
promising solution that ensures maximum
exploitation of already existing wind parks and
encourages new wind energy investments.
7
INVESTIGATION OF THE CAES SYSTEM(1/2)
More specifically, in a CAES system off-peak or
excess power, e.g. from a wind park, is used to
pressurize air into an appropriate air storage
facility via one or more compressors. Accordingly
, during times of peak load demand, the required
amount of air to cover the consumers load is
released from the cavern and supplied to a gas
turbine in order to generate guaranteed energy
amounts.
In this case, the stages of compression and
generation are separated and thus the entire
power of the gas turbine is available to satisfy
peak load demand. However, specific fuel
quantities are necessary.
8
INVESTIGATION OF THE CAES SYSTEM(2/2)
As far as the CAES system is concerned, it is
used in cases of large scale energy storage.
Except for pumped hydro storage, no other storage
system has a storage capacity as huge as CAES
(50-300 MW).
Also, the maximum storage period is among the
longest due to the fact that the pressurized air
losses are very low. The systems advantages
also include fast start ups (9-12 mins, much less
than the respective of conventional gas plants
25mins) and lower GHG emissions.
Also, the maximum storage period is among the
longest due to the fact that the pressurized air
losses are very low. The systems advantages
also include fast start ups (9-12 mins, much less
than the respective of conventional gas plants
25mins) and lower GHG emissions.
(Based on Sauer, 2006)
9
PROPOSED WIND-CAES SOLUTION THE CONCEPT
The proposed configuration is based on a dual
mode CAES system, i.e. a clutch is used to shift
to the compressor-turbine cycle.
When the amounts of wind energy stored in the
cavern cannot satisfy the guaranteed amounts of
energy, the system mode shifts from the CAES
cycle to the typical Brayton cycle, in order to
cover the load demand.
10
PROPOSED WIND-CAES SOLUTIONTHE MAIN COMPONENTS

• One or more existing wind parks, providing the
  wind energy rejections profile.
• An appropriate compressor used in order to
  pressurize air into a storage cavern by
  exploiting the wind energy surplus.
• An air storage cavern/tank of a given energy
  capacity, able to at least satisfy the guaranteed
  energy requirements on a daily basis.
• A gas turbine set operating either coupled with
  the compressor (CT cycle) or by utilizing the
  amount of compressed air on the basis of a CAES
  cycle.
• The BOS components including the intercooler, the
  preheater, the combustion chamber and an
  appropriate natural gas storage tank in order to
  meet the fuel requirements of the installation.

11
PROBLEM UNDER INVESTIGATION THE INPUTS
In the specific study, the wind energy
rejections profile (on an hourly basis) of a
25MW wind park operating in the east part of
Crete, is used. Additionally, during the
sizing procedure, the operational characteristics
and principles of all major components of the
CAES system (e.g. operational curves, efficiency
rates, etc.) are taken into account.
12
SIZING OF THE CAES CONFIGURATION
For the sizing of the proposed Wind-CAES
solution, a new numerical algorithm is developed
CAES-I. The main target of the sizing
methodology is the maximum exploitation of wind
energy rejections, without violating the 250/MWh
electricity production cost condition. Note that
the specific value is the current electricity
generation cost during peak load demand
periods. The two governing parameters during the
sizing procedure are the rated power of the
compressor and the hourly guaranteed amount of
energy. During the execution of the algorithm,
the compressor size is increased step by step, up
to the case that the maximum wind energy surplus
exploitation is fulfilled.
CAES-I Algorithm
13
PARAMETRICAL ANALYSIS RESULTS(1/3)
Maximum wind energy exploitation is achievable by
increasing the rated power of the compressor up
to 5MW. Besides, the magnitude of exploitation
is analogous to the amount of the guaranteed
energy provided by the system and the energy
storage capacity.
14
PARAMETRICAL ANALYSIS RESULTS(2/3)
Another important result is the significant
reduction of fuel consumption, compared with the
fuel consumption related to the classical cycle
operation. Higher levels of fuel savings (even
higher than 40) may be encountered when the
storage capacity becomes greater than the minimum
required.
15
PARAMETRICAL ANALYSIS RESULTS(3/3)
Another remarkable aspect is that given a
constant storage volume and allowing the increase
of energy provided to the local grid , the CAES
cycle contribution to the configurations energy
balance is minimized.
16
EVALUATION OF THE CAES SYSTEM ENERGY PRODUCTION
COST(1/4)
The total investment cost of the CAES
installation is a combination of the initial
installation cost and the corresponding
maintenance and operation costs (fixed
variable), expressed in present values.
The CAES investment becomes financially
attractive if the corresponding energy production
cost is less than the energy purchase price
offered by the local network operator during the
peak demand hours (250/MWh).
17
EVALUATION OF THE CAES SYSTEM ENERGY PRODUCTION
COST(2/4)
Using the optimum sizing results, the increase of
the gas turbine power implies higher utilization
of the storage capacity and suggests lower energy
production cost rates, even less than 200
Euros/MWh (?0).
18
EVALUATION OF THE CAES SYSTEM ENERGY PRODUCTION
COST(3/4)
Although a high capital cost should be
considered, high wind energy penetration is
obtained (even above 40 of the final energy
provided), while the electricity generation cost
of optimum configurations approaches 150/MWh.
19
EVALUATION OF THE CAES SYSTEM ENERGY PRODUCTION
COST(4/4)
By analyzing the total cost of the Wind-CAES
installation one may see that the fuel
consumption represents 1/3 of the total LC cost,
while the storage facility contributes by almost
25.
20
CONCLUSIONS

• An integrated evaluation methodology that is able
  to provide both the optimum sizing of a Wind-CAES
  system under the condition of maximum wind energy
  exploitation and investigating also the proposed
  systems cost-effectiveness has been developed.
• From the results obtained, the cost effectiveness
  of the proposed solution is validated, while the
  potential profitability implies rather attractive
  investment opportunities.
• Thus, by taking advantage of the forthcoming
  natural gas introduction and supporting further
  wind energy exploitation on the island of Crete,
  the proposed Wind-CAES configuration is thought
  to perfectly match the future electricity pattern
  and requirements of the island.
• Considering the gas turbines already operating in
  autonomous island networks, the concept of wind
  energy storage on the basis of a Wind-CAES
  configuration suggests increased levels of energy
  autonomy, cost effective energy solutions and
  minimization of electricity generation based
  pollution.